This invention relates to a picture block retransmission arrangement for use in a pattern or picture signal receiver as, for example, a facsimile receiver in requesting a counterpart transmitter to again transmit or retransmit a picture block signal, comprising a plurality of band-compression encoded picture line signals, as a retransmitted block signal which is for use in correcting errors found in the picture block signal transmitted to the receiver previous to the retransmitted block signal and is making the receiver receive such a picture block signal eventually with no or little error.
A picture block retransmission arrangement of the type described, is already known. For example, a method and an arrangement for facsimile picture transmission are disclosed in U.S. Pat. No. 4,223,356 issued to Gerhard Renelt et al and assigned to U.S. Philips Corporation.
In the manner known in the art, the picture line signals are representative of successive picture or scanning lines of an original pattern, respectively. The picture block signal represents a picture block of the original pattern which is transmitted from the counterpart transmitter to the receiver as a pattern or picture signal through a transmission path or channel between the transmitter and the receiver. Depending on the circumstances, the original pattern may consist of a picture block alone. The picture block signal may be said under the circumstances to represent the original pattern. At any rate, the transmission path is susceptible to disturbances, such as occurrence of noise, to have an inferior quality of introducing errors into the pattern signal. In this event, the picture block signal arrives at the receiver with one or more errors.
The receiver comprises a decoding circuit for decoding the picture block signal transmitted from the transmitter into a reproduced block signal. A picture block retransmission arrangement of the receiver requests the transmitter to again transmit the picture block signal as the above-mentioned retransmitted block signal whenever the errors of the reproduced block signal are not less in number than a predetermined number. The decoding circuit decodes the retransmitted block signal into another reproduced block signal. When it is desired to discriminate between the first-mentioned and the last-mentioned reproduced block signals by name, the first-mentioned reproduced block signal may be called a previous block signal. The last-mentioned reproduced block signal may be named a new block signal. In any event, each reproduced block signal comprises a plurality of reproduced line signals which are representative of the successive picture lines to correspond to the respective picture lines. As the case may be, each reproduced line signal of the new block signal will be referred to as an again reproduced line signal.
In the manner which will later be described in detail, a conventional picture block retransmission arrangement comprises a checking circuit for checking whether or not each reproduced block signal has errors. A retransmission requesting circuit requests the transmitter to again transmit the picture block signal whenever the errors are not less in number than a predetermined number. A substituting circuit substitutes the new block signal for the previous block signal on a block-by-block basis to produce a substituted block signal. The substituted block signal may have errors which are again not less in number than the predetermined number. In such an event, retransmission of the picture block signal must be requested again and again. A long transmission time is therefore necessary when the transmission path has an inferior quality. In a worst case, transmission of the original pattern does not converge, namely, never comes to an end.